In medical situations, it is sometimes necessary to remove screws, anchors, or other threaded members from bony tissues. The removal process may be difficult because of the general effects from implanting anchors (e.g. corrosion, fusion) and the particular effects of the patient's health (e.g. bone density, brittleness.)
Extreme rotational force is required to break these screws free from the bone during revision surgery, to such a degree that it is common for the tips of the driver to bend, twist, or otherwise deform, ultimately causing instrument failure.